Can't change someone who doesn't want to change. Definitely DON'T marry her, find the strength and LEAVE.
I think you need to let her go.You both need to talk and get to a stage where you tell her exactly how you feel.I believe that once a person cheats in a relationship it's for life & it very hard to forgive & you will certainly never forget.
If she is still cheating and has no desire to stop then you must end it,lots of people can get through and affair but others can't ,also the one who has been cheating should be the one making the effort to save the relationship,but if she is still doing it then she don't want this with you so I would run from this before you gets hurt anymore than you already are.
Hi there. I'm sorry. It is always so painful when our signficant other's cheat. It's almost hard to think straight. I think that you can walk away and find peace with that but you have to be ready to be out of this relationship. Are you ready for that?
if she is cheating on you NOW then you don't have much of a relationship and you should consider moving on. find a girl who won't cheat. that's what i'd do in your position.